manatee: Disable atuin open registration

hosts/manatee/modules/atuin/default.nix

@@ -16,7 +16,7 @@ in
       host = "0.0.0.0";
       inherit port;
       openFirewall = true;
-      openRegistration = true;
+      openRegistration = false;
       database.createLocally = true;
     };
   };